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International Journal of Aquaculture, 2014, Vol.4, No.09 55
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Xianping, 2002; Aralar et al., 2007). The potential use
of natural inland water bodies such as lakes and
reservoirs for the culture of this species has been
largely ignored.
At present, giant freshwater prawn
culturists in
Bangladesh have been facing a severe problem of
slower growth performance in culture condition.
Farmers claim that hatchery produced PLs do not
grow as fast as wild PLs. That’s why farmers are still
interested on the natural seed which effects on the
biodiversity. Although, at present, quite a large
quantity of the required seed of the species is being
collected from the nature; many hatcheries have, in
recent time, been established in the private sector. The
brood prawns required for the hatcheries are, in most
cases, obtained from the natural harvest from the
coastal rivers; there are instances of using broods from
the culture farms. Hatchery production and management,
inevitably warrants careful consideration for brood
selection and maintenance to mitigate the occurrence
of inbreeding that delays growth, feed conversion
efficiency, disease resistance etc. Little attention
however, has been paid to date to the genetic attributes
of this species (Aflalo et al., 2006; Thanh et al., 2009).
In order to reduce the pressure on the natural stocks of
this species, brood banking was initiated in some
coastal districts of Bangladesh. But this initiative was
in vain because of improper management. As the
hatchery owners buy only gravid fertilized egg
carrying females for seed production, farmers tended
to keep higher quantities of females in their brood
banks. Farmers maintained 1♂: 4♀ or 1♂: 5♀, even
1♂: 7♀ sex ratios in the brood banks. As a result, the
males were unable to fertilize the huge number of
females and the seeds produced were to be of poor
quality. Unfortunately, although several studies
provided valuable information regarding broodstock
management (Ling, 1969; Wickins and Beard, 1974;
Chow, 1982; Malecha, 1983; O’Donovan et al., 1984;
Chavez Justo et al., 1991; Damrong-phol et al., 1991;
Daniels et al., 1992), a more fine-focused genetic
approaches to improve stocks of cultured lines have
not yet been widely implemented. Thus, there is the
need for systematic breeding programs through
different genetic means in the future to improve
economically important traits in this species.
Significant productivity advances have been achieved
via selective breeding programs in aquaculture over
the last 10 years, particularly in a number of finfish
species where improvements of up to 10 to 20% per
generation have been achieved (Thanh et al., 2009).
The differential growth associated with different male
morphotypes is another problem for the culture of this
species which also warrants particular research
interest. Moreover, Mather and de Bruyn (2003)
reported that the productivity of
M
.
rosenbergii
in
Taiwan and Thailand has been declined due to
inbreeding depression of this species. For quality rich
seed production in hatcheries, it is the imperative to
develop a better brood stock with domestication where
the male and female ratio should be maintained at
appropriate combination. Increase of genetic
variability by maintaining different sex ratios would
be a plausible solution for increasing production of
prawn within a short time. Increase of heterozygosity
by this technique in farmed prawn, if possible, would
bring a revolution in prawn aquaculture in Bangladesh
creating a long lasting impact on the production
increase. The objectives of this current study were: - a)
to test the genetic variability of the PLs produced from
different sex ratios; b) to find out the best sex ratio for
the production of genetically variable and faster
growing seeds of giant freshwater prawn in
Bangladesh; and c) to improve the production potential
of a prime aquaculture species,
M. rosenbergii
through genetic means.
1 Materials and Methods
1.1 Experimental design
The experiment was conducted in the prawn hatchery
of “Fish Seed Multiplication farm (Gallamari, Khulna,
Bangladesh)”. Three different sex ratios were maintained
viz
., 1♂: 1♀, 1♂: 2♀ and 2♂: 1♀ respectively. A
control population was also kept that involved the
larvae production from the broods of natural source.
Three separate ponds and in total 450 prawns (both
male and female) were used in the trial. The prawns
were collected from the Kocha River, Pirojpur District,
Bangladesh. Mean body weight of the collected
prawns ranged between 20 to 25g. This study was
conducted from November 2010 to August 2011. The
adult prawns were stocked at the three separated
ponds for attaining maturation from November to May.
Then the berried females were collected from the ponds
and taken to hatchery. The larvae were reared under
hatchery condition for one month up to attaining the post
larvae stage (PL). Then, the larvae were brought to the